1. Field of the Invention
The present invention relates to a method for embedding and extracting a digital watermark on a lowest wavelet subband, and more particularly, to a method for embedding and extracting a digital watermark in which when a watermark is embedded on a lowest wavelet band (DC component region), the watermark is embedded depending on an embedment strength λ every position considering a human being's visual characteristic and embedment is selectively skipped to prevent screen deterioration such that robustness against an external attack is not only secured, but also a high screen quality watermarking is performed.
2. Description of the Related Art
Due to advent of a recent digital information age, as internet and various networks are widely spread and their related technologies such as data transmission, signal process technology and the like are developed, demand and its commercial value for various digital multimedia data such as audio, image, video and the like are increased. However, since various illegal copy and alteration become popularized along with the increased commercial value and demand, various studies for preventing the illegal copy to protect a copyright for a digital multimedia content are performed.
As such, as an effective method for protecting the digital copyright, a digital watermarking method is proposed. In the digital watermarking method, copyright information is embedded in multimedia data to the degree that a human being is difficult to perceive in visual sense, and when necessary, the copyright information can be extracted to check a copyrighter or a licensor. Accordingly, the watermarking should simultaneously secure invisibility for allowing whether or not the watermark is embedded not to be easily visible, and robustness for allowing to be against an external intended transformation, compression and image process, noise, etc.
However, it is difficult to secure the invisibility in a low frequency region due to a characteristic of a sensitive response of the human being's vision to a component variation of a low frequency than that of a high frequency, and the robustness is generally weaken in a high frequency region.
Accordingly, in the digital watermarking method, it is an important matter that the robustness is not only provided against the external attack or noise, etc., but also the screen deterioration is minimized.
On the other hand, the watermarking method using a conventional wavelet transformation generally employs a method for embedding the watermark on remaining subbands (high frequency region and intermediate frequency region) excepting for an LL subband so as to secure the invisibility.
However, according to a recent appearance of a high compression technology such as JPEG2000, the conventional watermarking method has a drawback in that the robustness is weaken against the high compression, the external intended attack and the like.
Accordingly, it is required to embed the watermark on the DC component region being the lowest wavelet subband, and as a result, in case the watermark is embedded on the LL subband, it is anxiously required to minimize the screen deterioration to secure the invisibility.